MRAM cells using the so-called self-referenced reading operation typically comprise a magnetic tunnel junction formed of a magnetic storage layer having a magnetization which direction can be changed from a first stable direction to a second stable direction, a thin insulating layer, and a sense layer having a magnetization with a reversible direction. Self-referenced MRAM cells allows for performing the write and read operation with low power consumption and an increased speed. Moreover, self-referenced MRAM cells are useful for making functional memories having a reduced yield as well as for high temperature and security applications.
However, a dipolar coupling between the storage and sense layers occurs due to local magnetic stray field, coupling the magnetization of the sense layer with the one of the storage layer in a closed magnetic flux configuration. Switching the sense layer magnetization will then require applying a magnetic field high enough to overcome the dipolar coupling. The dipolar coupling results in a shift (or bias) of the hysteresis loop when applying a field cycle to measure the hysteresis loop of the sense layer. This dipolar coupling depends on the thickness and magnetization of the storage and sense layers, and on the size of the magnetic tunnel junction. In particular, dipolar coupling increases with decreasing the magnetic tunnel junction diameter and can thus become a major issue when scaling down the MRAM cell.
The stray field generated by the storage layer on the sense layer results in increasing power consumption, especially during the read operation of the MRAM cell. Moreover, decreasing the stray field, for example using a synthetic storage layer, can result in an increase in the switching field of the magnetization of the sense layer.